Monitoring Varroa Mites
Varroa mites are one of the most significant threats to honey bee health today. Mites reproduce quickly and spread lethal viruses from bee to bee. The only way to control the deadly effects of viruses is to control the mites. Without proper management, mite-infested colonies have a very high probability of dying. Mites can also spread from colony to colony, on the backs of robbing and drifting bees, within a one-mile radius. If you don't monitor and manage mites, you may be putting your neighbors' bees at risk. In urban areas, horizontal mite transmission (spreading mites) is a serious threat to honey bee health. Read more about varroa mites here.
The Bee Squad encourages all beekeepers to monitor varroa populations in their colonies. Regular mite testing throughout the beekeeping season informs beekeepers when mite mitigation is necessary.
The two primary methods of sampling adult bees to estimate mite levels in a colony are the powdered sugar roll and alcohol wash.
Powdered Sugar Roll University of Nebraska developed a testing method called the “powdered sugar roll” where most of the bees in the sample survive (unless the bees get wet or are shaken too hard). Avoid using the powdered sugar roll in humid weather or if the bees are bringing in lots of nectar as the powdered sugar can dissolve and become sticky. In an effort to make mite monitoring easier, the Bee Squad put together a powdered sugar mite testing kit called "MiteCheck Kit." These kits are reusable and come with detailed user instructions.
Alcohol Wash The alcohol wash mite sampling method is more reliable with fewer variables that affect the efficacy as compared to the powdered sugar roll test (e.g., humidity that results in the sugar sticking to the bees, how hard the bees are shaken). For simple instructions on the alcohol wash see this guide. MiteCheck kits can easily be adapted for an alcohol wash. All you need is rubbing alcohol from a drug store and a solid canning jar lid. Dish soap can also be used instead of alcohol, however the mites can be difficult to see through the suds when using this straining method.
How low should mite populations be in your colony?
Whether you use the powdered sugar roll or alcohol wash sampling method, mite levels should be kept below 1 mites per 100 bees in the spring and 2 mites per 100 bees the rest of the year. The goal is to keep mite levels low year round.
Treating for Varroa Mites: When & What?
All successful beekeepers manage varroa mites--it can’t be avoided. There are many ways to manage mites, some more complicated than others. This guide is intended for beekeepers who need a basic, tried and true method to keep their bees alive. As you build confidence and skill as a beekeeper, it is easier to experiment with other management methods that require advanced techniques and knowledge of bee biology. Use the recommendations below to manage mite populations in Minnesota honey bee colonies. For instructions on HOW to apply treatments, see the Honey Bee Health Coalition page on varroa management.
The most effective time to employ a miticide is in a broodless colony when all the mites are on adult bees. Mites on adult bees are more easily killed; mites in brood are difficult to get rid of because the wax cappings on the brood cells protect the mites as they reproduce underneath. The hardest time control mite populations is when the colony has lots of brood. A spring mite control will help reduce the likelihood of high mite levels in late summer, when large brood nests make it hardest to control mite populations effectively.
In May, June, August, and September, monitor varroa mites. Sample after a treatment to confirm that it was effective.
The below biology-based treatment schedule has been an effective method for us to manage mite populations in our colonies. However, we cannot guarantee your colonies will not have issues with mites using this method. Monitoring often will help you catch unexpected spikes in your mite populations, and adjust your treatment plan accordingly.
- Package (suggested): Treat with oxalic acid or Hopguard® 5 to 7 days after installing the package.
- Nuc: Ask the supplier if and how they managed mites in the spring. If they did not manage mites, use a miticide as you would an overwintered colony once the bees occupy a full deep box.
- Overwintered colony: treat with Mite Away Quick Strips®, Formic Pro®, or Apiguard®. Mite Away Quick Strips® and Formic Pro® can be applied when honey supers are on the colony; other treatments must be complete before honey supers are applied.
- Avoid treating colonies unless mite levels are above 2 mites per 100 bees. Use Mite Away Quick Strips® or Formic Pro® as these products are safe to use with honey supers.
Before August 20
- Remove supers and treat with Mite Away Quick Strips®, Formic Pro®, Apiguard®, or ApiLife VAR®
- Check mites after treatment and every two weeks in fall to see that the treatment worked and if there is mite re-infestation from nearby colonies.
Fall when no brood is left in the colony
- Treat with oxalic acid dribble or vapor in late fall. Can use HopGuard® instead, but remove the strips before winter.
Guidance on Using Mite Treatment Products
The below chart shows when each of the registered products can be used as mite control. Using the products when they are most effective can reduce the overall number of treatments needed. Always read and follow the label.
*Information on Certified Applicator License from the EPA.
**Oxalic acid vapor can be effective, but research suggests at least 2g oxalic acid per box is needed for the best efficacy, which is more than the label rate of 1g oxalic acid per brood box.